Qt: fix album Art update

Master and branch have diverged a bit more than I thought, on this
matter.

modules/gui/qt4/components/interface_widgets.cpp

@@ -519,9 +519,11 @@ CoverArtLabel::CoverArtLabel( QWidget *parent, intf_thread_t *_p_i )
     CONNECT( action, triggered(), this, askForUpdate() );
     addAction( action );
 
-    p_item = THEMIM->currentInputItem();
+    input_item_t *p_item = THEMIM->currentInputItem();
     if( p_item )
-        showArtUpdate( p_item );
+    {
+        showArtUpdate( THEMIM->getIM()->decodeArtURL( p_item ) );
+    }
     else
         showArtUpdate( "" );
 }